Analyze biochemical and physical parameters of your protein sequences
Input Protein Sequence
Only standard amino acid characters are accepted.
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Our Protein Extinction Coefficient Calculator is a comprehensive, web-based tool for analyzing the essential biochemical and physical properties of your protein sequences. By simply inputting a sequence, you can instantly generate a detailed analysis, including the molar extinction coefficient, molecular weight, theoretical pI, amino acid composition, and more. This tool helps you accurately determine protein concentration from UV absorbance data, predict protein behavior across various biochemical assays, and gain critical insights for downstream applications such as protein purification, spectroscopy, and structural analysis.
How to Use
- Input Sequence: Paste your protein sequence into the text box. The sequence should contain only standard single-letter amino acid codes.
- Analyze: Click the “Analyze Sequence” button to process your data.
- Review Results: The tool will instantly display a comprehensive report of the calculated parameters for your protein.
Tip: Before pasting, ensure your sequence is in a plain text format and does not contain any headers, numbers, or non-standard characters for the most accurate results.
How is the Protein Extinction Coefficient Calculated?
The protein extinction coefficient is a measure of how much light a protein absorbs at a specific wavelength, typically 280 nm. This value is crucial for determining protein concentration using a spectrophotometer, based on the Beer-Lambert law (A=εlc).
The calculation is based on the contributions of the aromatic amino acids—Tryptophan (Trp) and Tyrosine (Tyr)—and the sulfur-containing amino acid Cysteine (Cys), which are the primary absorbers of UV light at 280 nm. The molar extinction coefficient (ε) is calculated using the following formula, based on the number of each of these residues (n) in the sequence:
ε_280(M−1cm−1)=(n_Trp×5500)+(n_Tyr×1490)+(n_Cys×125)
This formula assumes all cysteine residues appear as cystine (in disulfide bonds). The tool provides two values: one assuming all cysteines are reduced and one assuming all form cystine bridges.
Features and Outputs
This protein parameters analyzer provides the following comprehensive outputs:
- Amino Acid Composition: Delivers the absolute count and percentage frequency for each of the 20 standard amino acids in your sequence.
- Molecular Weight (MW): Calculates the protein’s molecular weight based on the average isotopic masses of its constituent amino acids and the assumption of a single H₂O molecule at the termini.
- Theoretical Isoelectric Point (pI): Estimates the pH at which the protein carries no net electrical charge, a critical parameter for purification methods like isoelectric focusing.
- Amino Acid Property Groups: Classifies and sums amino acids based on their chemical properties (e.g., Hydrophobic, Polar, Positively Charged, Negatively Charged) to give an overview of the protein’s character.
- Atomic Composition: Provides the total count of each atom type (Carbon, Hydrogen, Nitrogen, Oxygen, Sulfur) that makes up the protein molecule.
- Extinction Coefficient: Estimates the molar absorption coefficient of the protein at 280 nm, essential for determining protein concentration via UV spectroscopy. Values are provided for both reduced and oxidized cysteine states.
- Estimated Half-Life: Predicts the protein’s stability and lifespan within different biological systems, offering in-vitro estimates for mammalian reticulocytes, yeast, and E. coli.
- Instability Index: Computes a score to predict the protein’s stability in a test tube. A value below 40 suggests a stable protein, while a value above 40 indicates potential instability.
- Aliphatic Index: Calculates the relative volume of the protein occupied by aliphatic side chains (Alanine, Valine, Isoleucine, and Leucine), a positive indicator of thermostability.
- Grand Average of Hydropathicity (GRAVY): A score representing the overall hydrophobicity of the protein. Positive values indicate a more hydrophobic protein, while negative values suggest a more hydrophilic one.
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FAQ
References & Suggested Reading
This tool was developed in line with established principles of computational biochemistry to ensure accurate, reliable results. The resources listed below are the foundational research and key papers that define these standards, and we highly recommend them for a deeper understanding of the scientific principles.
- Gill, S. C., & von Hippel, P. H. (1989). Calculation of protein extinction coefficients from amino acid sequence data. Analytical Biochemistry, 182(2), 319–326. https://doi.org/10.1016/0003-2697(89)90602-7
- Gasteiger, E., Hoogland, C., Gattiker, A., Duvaud, S., Wilkins, M. R., Appel, R. D., & Bairoch, A. (2005). Protein identification and analysis tools on the ExPASy server. In J. M. Walker (Ed.), The Proteomics Protocols Handbook (pp. 571–607). Humana Press. https://doi.org/10.1385/1-59259-890-0:571
Meet the Authors
Mahdi Morshedi Yekta
Founder & Bioinformatics Developer
Mahdi is the founder of ScienceCodons and a Medical Biotechnologist with a deep passion for computational biology. Holding an M.Sc. in Medical Biotechnology, he specializes in transforming complex biological algorithms into accessible, high-performance web tools, bridging the gap between laboratory sciences and software engineering.
Fatemeh Faryadras
Medical Biotechnologist & Researcher
Fatemeh is a Medical Biotechnologist and researcher. With extensive expertise in genetic engineering, molecular cloning, and cancer biology, she combines her rigorous laboratory background with intuitive design principles to create reliable, user-centered scientific calculators and tools.
Dr. Mosayeb Rostamian
Assistant Professor, Infectious Diseases Research Center
Certified Scientific Reviewer
Google ScholarExpert Review Process
To ensure the highest quality and scientific accuracy, this tool's underlying algorithms, formulas, and edge-case handling have been thoroughly reviewed and validated by Dr. Mosayeb Rostamian.
The "Reviewed By" badge signifies that an independent expert has evaluated the tool's logic to guarantee accuracy and alignment with the current consensus in the scientific community.